Speeds of traveling vehicles can be measured via radar or laser. A normal radar gun used by law enforcement agencies sends out a radio pulse and waits for the reflection. It then measures the frequency shift in the signal and uses the Doppler effect to determine the speed of the vehicle. Speed guns based on lasers also can measure vehicle speed, but they rely on the reflection time of light rather than the Doppler effect.
Rotational speeds of engines and turbochargers are measured by either sensing the resulting structural vibrations using a vibration sensor such as an accelerometer, or by using a non-contact strobe-based tachometer, when a rotating surface is visible. When a rotating surface is not visible, the strobe-tachometer cannot be used.
Different kinds of monitoring systems have been used to monitor traffic with the most prevalent system being a roadway metal detector. In such system, a wire loop was embedded in the roadway and its terminals were connected to detection circuitry that measured the inductance changes in the wire loop. Because the inductance in the wire loop was perturbed by a motor vehicle (which included a quantity of ferromagnetic material) passing over it, the detection circuitry detected when a motor vehicle was over the wire loop. Based on this perturbation, the detection circuitry created a binary signal, called a “loop relay signal”, which was transmitted to the command center of the highway department. The command center gathered the respective loop relay signals and from these made a determination as to the likelihood of congestion. The use of wire loops was, however, disadvantageous for several reasons.
First, a wire loop system did not detect a motor vehicle unless the motor vehicle included sufficient ferromagnetic material to create a noticeable perturbation in the inductance in the wire loop. Because the trend now is to fabricate motor vehicles with non-ferromagnetic alloys, plastics and composite materials, wire loop systems will increasingly fail to detect the presence of motor vehicles. It is already well known that wire loops often overlook small vehicles. Another disadvantage of wire loop systems was that they were expensive to install and maintain. Installation and repair required that a lane be closed, that the roadway be cut and that the cut be sealed. Often too, harsh weather precluded this operation for several months.
Non-invasive traffic monitoring systems have been suggested, among them being U.S. Pat. No. 3,445,637, patented May 20, 1969 by J. M. Auer, Jr., provided apparatus for measuring traffic density in which a sonic detector produced a discrete signal which was inversely proportional only to vehicle speed for each passing vehicle.
U.S. Pat. No. 3,920,967, patented Nov. 18, 1975, by D. T. Martin et al, provided a computerized traffic control apparatus for controlling the flow of vehicular traffic through a network of intersections. Detectors in proximity to selected intersections generated electrical signals which were representative of the commencement and termination of vehicle presence. One or more field preprocessors received these signals and responsively generated secondary signals which were representative of vehicle count and speed. These secondary signals were transmitted to a computer which analyzed them and responsively generated control signals which were transmitted to, and governed, the sequential operation of traffic signal heads at controlled intersections.
U.S. Pat. No. 4,806,931, patented Feb. 21, 1985, by T. M. Nelson, provided a sound pattern discrimination system. The patented system was provided for the detection and recognition of pre-established sound patterns, e.g., the various patterns produced by the sirens of emergency vehicles. Directional information along with the output of a Schmitt trigger was supplied to a microprocessor which was used to control the signal lights at an intersection in response to the detected siren.
U.S. Pat. No. 5,060,206, patented Oct. 22, 1991 by F. C. de Metz Sr., provided a marine acoustic detector for use in identifying a characteristic airborne sound pressure field which was generated by a propeller-driven aircraft.
U.S. Pat. No. 5,008,666, patented Apr. 16, 1991, by F. J. Gebert et al., disclosed traffic measurement equipment employing a pair of coaxial cables and a presence detector for providing measurements including vehicle count, vehicle length, vehicle time of arrival, vehicle speed, number of axles per vehicle, axle distance per vehicle, vehicle gap, headway and axle weights.
U.S. Pat. No. 6,204,778 issued to Bergan et al. on Mar. 20, 2001, uses electro-acoustic sensor arrays that are specifically mounted above the road to sense the sounds produced by motor vehicles as they pass under the sensor arrays. The arrays are used to detect when a vehicle is within the zone under the sensor arrays. The system determines if the motor vehicle is a truck by comparing the MAGNITUDE of the sound within a predetermined frequency band to a threshold level using a band-pass filter. The speed of the vehicle is determined by the length of time for the vehicle to enter the detection zone of the above-road electro-acoustic sensor arrays thereby teaching a vehicle speed detection method that is acoustic-based and dependent on the MAGNITUDE of the vehicle's sound within a predetermined frequency band.